<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
</head>
<body>
<script>
    var a1 = ['1', '2', '3'];
    for (var i = 0; i < a1.length; i++) {
        console.log(a1[i]);
    }
    a1.forEach(function (a) {
        console.log(a);
    })

    var a2 = a1.map(function (a) {
        return a + "你好";
    })
    console.log(a2);

    for (var a in a1) {
        console.log(a1[a]);
    }
</script>
</body>
</html>